LAUSANNE, Switzerland -- Iranian Foreign Minister Mohammad Javad Zarif says there has been "significant progress" but no "final result yet" at talks aimed at reaching a deal on Tehran's nuclear program.

Zarif spoke on April 2 as senior diplomats from six global powers and Iran continued talks despite missing a March 31 deadline for the outlines of a deal to rein in Iran's nuclear activities in exchange for relief from painful economic sanctions.

Western nations want to ensure Iran cannot build a nuclear bomb, while Tehran wants a swift end to UN, U.S., and European Union sanctions that have badly hurt its economy.

"We have made significant progress in the talks but still we have not agreed on the reviewed solutions," said Zarif, who met for hours overnight with U.S. Secretary of State John Kerry while lower-level officials also held talks.

"We are working on setting parameters of the issues that will led to drafting the final deal by end of June," Zarif said in a reference to the June 30 deadline the six powers and Iran have set for a comprehensive deal.

Negotiators from Iran and the six powers -- the United States, Russia, China, Britain, France, and Germany -- also held a series of meetings into the morning.

"For those keeping track, it's 6 a.m. in Lausanne. That was truly an all-nighter," State Department spokeswoman Marie Harf said on Twitter.

Nearly five hours later, she tweeted that Kerry and other negotiators were "back at work."

German Foreign Minister Frank-Walter Steinmeier also stayed in Lausanne after the deadline passed, and a German diplomat said he was calling off a planned visit to the Baltics to remain at the talks.

French Foreign Minister Laurent Fabius returned late on April 1 after flying back to Paris the previous day because progress had been too slow.

"We are a few meters from the finishing line, but it's always the last meters that are the most difficult. We will try and cross them," Fabius said upon on his return to the Swiss resort city.

He added, "We want a robust and verifiable agreement and there are still points where there needs to be progress especially on the Iranian side."

White House spokesman Josh Earnest told reporters in Washington that "the time has come for Iran to make some decisions."

But Iran's Zarif said it was the major powers that must budge, not Tehran.

"Progress and success of the talks depends on the political will of the other party," Zarif said on April 1, adding that "this is an issue they have always had a problem with."

Negotiators have been wrangling over the scope of uranium enrichment Iran would be allowed to conduct, where stockpiles of enriched uranium should be stored, proposed limits on Iran's nuclear research and development, and the timing and conditions for the removal of sanctions.

The five permanent UN Security Council nations and Germany are seeking verifiable curbs on Iran's nuclear program that ensure Tehran is not able to develop nuclear weapons.

Securing a comprehensive deal after more than two decades of tension over Iran's nuclear program would improve the chances of rapprochement between Iran and the United States, whose relations have been badly strained since the Middle East country's 1979 Islamic Revolution.

But conservatives in both the United States and Iran are extremely wary of a deal, as are U.S. allies Israel and Saudi Arabia.

An interim deal was reached in November 2013, but negotiators have missed two self-imposed deadlines for a comprehensive agreement since then.

Iran says its nuclear program is for purely peaceful purposes, mostly power generation, and it wants U.S., EU, and UN sanctions lifted swiftly.

The six powers hope to ensure that for at least the next 10 years, Iran is at least one year away from being able to produce enough fissile material for an atomic weapon, and they want Iran's most sensitive nuclear work to be suspended for more than a decade.

Officials from both sides have said the main sticking points were the removal of the UN sanctions, the rules for reimposing them if Tehran fails to adhere to the deal, and Iranian demands for the right to unfettered research and development into advanced nuclear centrifuges after an initial 10-year period covered by the potential agreement expires.

With reporting Hannah Kaviani of RFE/RL's Radio Farda in Lausanne, AP, and Reuters